Abstract

Markup languages such as HTML [HTML401] and SVG [SVG11] provide a style attribute on
most elements, to hold inline style information that applies to those
elements. One of the possible style sheet languages is CSS. This draft
describes the syntax and interpretation of the CSS fragment that can be
used in such style attributes.

Status of this document

This section describes the status of this document at the time of
its publication. Other documents may supersede this document. A list of
current W3C publications and the latest revision of this technical report
can be found in the W3C technical reports
index at http://www.w3.org/TR/.

A Candidate Recommendation is a document that has been widely reviewed
and is ready for implementation. W3C encourages everybody to implement
this specification and return comments to the (archived) public
mailing list
www-style@w3.org (see instructions). When sending
e-mail, please put the text “css-style-attr” in the subject,
preferably like this: “[css-style-attr]
…summary of comment…”

Publication as a Candidate Recommendation does not imply endorsement by
the W3C Membership. This is a draft document and may be updated, replaced
or obsoleted by other documents at any time. It is inappropriate to cite
this document as other than work in progress.

For this specification to exit the CR stage, the following conditions
shall be met:

There must be at least two interoperable implementations. For the
purposes of this criterion, we define the following terms:

interoperable

passing the respective test case(s) in the CSS test suite, or, if
the implementation is not a Web browser, an equivalent test. Every
relevant test in the test suite should have an equivalent test created
if such a user agent (UA) is to be used to claim interoperability. In
addition if such a UA is to be used to claim interoperability, then
there must one or more additional UAs which can also pass those
equivalent tests in the same way for the purpose of interoperability.
The equivalent tests must be made publicly available for the purposes
of peer review.

implementation

a user agent which:

implements the specification.

is available (i.e. publicly downloadable or available through some
other public point of sale mechanism). This is the "show me"
requirement.

is shipped, or is a "nightly build" (i.e., a development version
for the next release), but is not experimental (i.e., a version
specifically designed to pass the test suite and not intended for
daily usage going forward).

A minimum of one month of the CR period must elapse. That is, this
specification will not exit CR before 14 November 2010. When the
specification exits CR, an implementation report will be published. At
this point, no such report exists.

A CSS Style Attributes Test
Suite will be developed during the Candidate Recommendation phase of
this CSS Style Attributes specification.

Table of contents

1. Introduction

Some document formats have a style
attribute to permit the author to directly apply style information
to specific elements in documents. If a document format defines a style
attribute (whether named ‘style’
or something else) and the attribute accepts CSS as its value, then this
specification defines that style
attribute’s syntax and interpretation.

The following example shows the use of the style attribute
in HTML [HTML401]:

<p style="color: #090; line-height: 1.2">...</p>

2. Conformance

A document or implementation cannot conform to CSS Style Attributes
alone, but can claim conformance to CSS Style Attributes if it satisfies
the conformance requirements in this specification when implementing CSS
together with style attribute handling as defined in a document language
that has one or more CSS style attributes.

Conformance to CSS Style Attributes is defined for two classes:

document

A document represented in a document language that defines a style
attribute for one or more of its elements.

interpreter

Someone or something that interprets the semantics of a document and
its associated style information. (Most CSS user agents
fall under this category.)

The conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
document are to be interpreted as described in RFC 2119. However, for
readability, these words do not appear in all uppercase letters in this
specification. All of the text of this specification is normative except
sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words "for
example" or are set apart from the normative text with
class="example", like this:

This is an example of an informative example.

Informative notes begin with the word "Note" and are set apart from the
normative text with class="note", like this:

Note, this is an informative note.

3. Syntax and Parsing

The value of the style attribute must match the syntax of the contents
of a CSS declaration
block (excluding the delimiting braces), whose formal grammar is given
below in the terms and conventions of the CSS core
grammar:

declaration-list
: S* declaration? [ ';' S* declaration? ]*
;

Note that following the CSS2.1 convention, comment tokens are
not shown in the rule above.

The interpreter must parse the style attribute's value using the same
forward-compatible parsing rules that apply to parsing declaration block
contents in a normal CSS style sheet. See chapter 4 of the CSS2.1
specification for details. [CSS21]

Note that because there is no open brace delimiting the
declaration list in the CSS style attribute syntax, a close brace
(}) in the style attribute's value does not terminate the
style data: it is merely an invalid token.

4. Cascading and Interpretation

The declarations in a style attribute apply to the element to which the
attribute belongs. In the cascade, these declarations are considered to
have author origin and a specificity higher than any selector. CSS2.1 defines how
style sheets and style attributes are cascaded together. [CSS21] Relative URLs in the style
data must be resolved relative to the style attribute's element (or to the
document if per-element resolution is not defined) when the attribute's
value is parsed.

Aside from the differences in cascading, the declarations in a style
attribute must be interpreted exactly as if they were given in a CSS style
rule that applies to the element.

The CSS Working Group strongly recommends that document languages do not
allow multiple CSS style attributes on a single element. If a document
language allows multiple CSS style attributes, each must be parsed
independently and treated as a separate style rule, the ordering of which
should be defined by the document language, else is undefined.